Combined waste-heat boiler and chemical recovery unit



May 1, 1951. D. DALlN 2,550,676

COMBINED WASTE HEAT BOILER AND CHEMICAL RECOVERY UNIT Fild- Oct. 17, 1945 2 Sheets-Sheet 1 PREHEHTERS D. DALIN COMBINED WASTE HEAT BOILER AND CHEMICAL REco ERY UNIT Filed Oct. 17, 1945 Z Sheet's-Sheet'Z 3M DEX/1U: aim

Patented May 1, 1951 COMBINED WASTE-HEAT BOILER AND CHEMICAL RECOVERY UNIT David Dalin, Sodertalje, Sweden Application October 17, 1945, Serial N 0. 622,832 1 In Sweden June 20, 1945 This invention relates to the recovery of valu- B,b1 constituents of waste liquors such as the recovery of sodium sulphide from". black liquor, and to furnace apparatuses used in this process.

The general object of this invention is twofold. First, it is the purpose of this invention to provide an improved furnace. apparatus especial.-

{ ly suitable for use in black liquor recovery processes but also of considerable value in furnaces of general utility; and second, this invention contemplates an improvement in the art of processing. waste liquors to recover valuable chemical constituents thereof.

- The presence of fly-ash in combustion gases and accummulating on the surfaces of heat. exchangers over which the combustion gases flow has long presented a troublesome problem. The 1 removal of the. fiy-ash or soot from the heat exchange surfaces has generally been effected in the past by means of soot blowers arranged to direct blasts of compressed air or steam against the surfaces to be. cleaned. This past method is 7 only partly effective especially when the soot or fly-sash consists of material that is exceedingly sticky, as. for instance, the fly-ashj entrained in the combustion gases of smelting furnaces. Such flye'ash has a tendency to. bake on the surfaces itadheres to so that it is often impossible to remove it. by blasts. of air orsteam. In such instances mechanical means must be used for cleaningthe surfaces involved.

I The present invention overcomes these objece tionsthrough the provision of a, novel arrangement. of the heat exchange, surfaces with respect to. the direction of gas. flow thereover and through periodic. agitation or shaking of the heat exchange surfaces.

Toi thisqend it is an object. of this. invention to provide a furnace. of the character described wherein heat. absorbing and dissipating members "arjeloosely mounted or supported in the path of the combustion gases to be. impinged by the flyexchange, surfaces on which the accumulation of fly-ash and soot occurs as. serpentine tubes or ducts. ailing elon ated substantially vertical p01.- tions and to loosely dra e thesetubes orducts Qversu able supporting: structures so: as to en'- ablegviolent agitation or shaking of the. tubes 4 Claims. (01. ass-262 from.

. to dislodge accumulated fly-ash and soottheree In the process 'of treating black liquorand other waste liquors for the recovery of their valuable chemical constituents, various methods have been proposed and employedin the past. One of the methods heretofore found generally satisfactory has been .to spray evaporated waste liquor into a combustion chamber where the organic constituents of the black liquor burn and the constituents sought to .be recovered are dis.- charged from the bottom of the combustion chamber asaliquid.

Difficulty has been experienced, however, with this previous method of recovering chemical constituents of waste liquors, due to the clogging of the gas passages by the adherence of the sticky fly-ash on the surfaces of the heat exchangers by which the-heat .of the process is utilized for steam generation and other usefut purposes. The difficulties resulting from the adhesion of the fly-ash of this process on the. heat exchange surfaces can be readily appreciated fromthefact that. until cooled down to'a temperaturebelow thirteen hundred degrees Fahrenheit (1300? F.) this fly-ash will stick to everything with which it comes in contact.

With a. view toward overcoming this disadvantage the present invention has as. another of its objects an entirely new manner of handling the fly-ash entrained in the combustion gases whereby the, fly-ash is deliberately intercepted and accumulated on fluid cooled surfaces whichv not only enable useful'utilization of the. heat generated but are so arranged that the accumulated fly-ash may be easily dislodged therefrom.

In this connection, it is a. further object of this invention to so locate the intercepting surfaces that the fiy-ash which does not adhere thereto is frozen to reduce its tendency to stick to sube sequently encountered surfaces as it leaves the combustion chamber.

Another object of this invention is to provide a more compact furnace unit made possible through the utilization of a novel arrangement of gas passages which enables material reduction in the height of the unit.

Another object of'this invention is to provide a gas passagev so constructed that separation of the entrained frozen less sticky fly-ash particles is materially facilitated and promoted by an abrupt change in direction of the flow of com bustion gases.

With the above and other objects in view which will appear as thedescription proceeds, this in:

The accompanying drawings illustrate one complete example of the physical embodiment of the invention constructed in accordance with the best mode so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a vertical sectional view through a furnace apparatus embodying this invention;

Figure 2 is a perspective view illustrating. a por- 23. Each of these collecting hoppers has a screw conveyer 24 in its bottom whereby the material accumulated in the collecting hoppers may be continually discharged into a duct (not shown) or other suitable means by which it is conveyed back to the combustion chamber to be reprocessed.

Attention is directed to the fact that the positioning of the first collecting hopper 2| under the verical or the upright section It of the gas pass facilitates the separation of solid particles entrained in the combustion gas by virtue of their tendency to continue downward as the combustion gases abruptly change direction from downward to horizontal.

Beyond the finalheat exchanger 20 the gas pass continues through serially arranged air tion of the novel heat exchanger of this invention showing the manner in which its component parts are loosely supported to be agitated or shaken;

Figure 3 is a fragmentary detail sectional view. taken on the plane of the line 33 of Figure 2 to more accurately illustrate the actual spacing of the heat exchanger; and Y Figure 4 'is a cross sectional view through the combustion chamber, said view being taken on the plane of the line 4-4 in Figure 1.

Referring now more particularly to the accompanying'drawings in which like numerals indicate like parts, the numeral 5 designates generally an upright combustion chambervthe walls of which are lined with vertical boiler tubes 6. The front and side walls of the combustion chamber continue unbrokenly for their entire height, .but the rear wall I terminates short of the top or the ceiling to provide an opening through which gases leave the combustion chamber. To enable the'combustion gases to pass through this opening alternate ones of the boiler tubes lining the rear wall I are offset rearwardly as at 8 to provide adequate spacing between adjacent tubes.

It is, of. course, understood that all of the boiler tubes 6 are suitably connected with a steam drum Qand thatthe circulation through these tubes may be natural or forced.

The bottom of the combustion chamber has a lining in of heat insulating material capable of withstanding. the high temperature and the chemical reaction taking. placetherein, and has a spouted outlet ll leading therefrom through which the chemicals sought to be recovered flow asa -liquid. I.The liquid thus discharged from the bottom of the combustion chamber flows into a tank I2 or may be conducted to any other desired reservoir or place of use. 1

The exit for the combustion gases in the upper portion of the .combustion chamber provides the inlet of a gas pass indicated generally by the numeral l4 and along which the combustion gases flow to be subsequently discharged to the stack. The gas pass 14 is substantially right-angular and has an upright section t5 overlying the back wall of the combustion chamber and of substantially the same height as the combustion chamber. At its bottom the upright section of the gas pass connects with a substantially horizontal section IS in which a plurality of serially arranged heat exchangers ll, l8, l9 and are located.

At the juncture of the upright and substantially horizontal sections of the gas pass and extending under the upright section, is a collecting hopper 2|. 1 Similar collecting hoppers 22 and 23 are disposed under the heat exchangers l8, l9 and (ill preheater-s 25 and 2B, the latter of which preferably has a cast iron housing to more successfully withstand the acids which develop at this stage of the process. After leaving the air preheater 26 the combustion gases continue along a duct 21 to the stack.

Though thespecific arrangement of the air preheaters forms no part of this invention, it should be noted that air is admitted thereto through an inlet duct 28, passes through the preheater 26 and from there,'through a duct 29 to the inlet of the air preheater 25. The outlet of the air preheater 25 discharges into a duct 30 which leads forwardly to the combustion chamber to provide primary and secondary combustion air.

The primary combustion air enters the combustion chamber through ports 3| fed from the duct 30 through suitable valved branch ducts 32. Secondary combustion air enters the combustion chamber through ports 33 and 3d supplied by suitable valved branch ducts 35 and 36 respectively.

At an elevation between the lower and upper secondary air admission ports 33 and 34, respectively, injection nozzles 31 project through the opposite side walls of the combustion chamber. Thewaste liquor to be processed is sprayed into the combustion chamber through these inection nozzles 3'l,it being understood that the waste liquor is first'substantially evaporated'and that it is forced through the nozzles at high pressure.

After the combustion chamber is initially heated, either by means of an oil burner (not shown) or by building a fire in the bottom of the chamber, the process is self-regenerative as the organic matter contained in the waste liquor sprayed into the combustion chamber burns with a hot flame. As the process proceeds the chemical constituents of the waste liquor sought to'be recovered are liquified and flow from the bottom of the combustion chamber. Much of the chemicals sought to be recovered, however, are carried along by the combustion gases as fly-ash. This fly-ash, as hereinbefore noted, due to its high temperature, is quite sticky and will adhere to any surface with which it comes in contact. This is particularly so in the recovery of sodium sulphide from black, liquor. i

Totrap the fly-ash ina manner which will enable easy recovery of the valuable chemical constituents thereof, an intercepting unit in the form of a heat exchanger 38 of novel design is mounted in the top of the combustion chamber adjacent to the point of communication between the combustion chamber'and'the gas pass M. This heat exchanger 38 consists of a plurality of side-by-side serpentine tically down into the combustion chamber.

The support for these coils comprise a plu rality of substantially'horizontal parallel spaced tubes 40. The tubes may connect the steam drum 9 with a header 4| for the upper ends of coils or tubes 39 loosely ,1 suspended at their upper ends and hanging yer.-

the boiler tubes 6 overlying the front wall of the draped over the secondary supporting tubes 42 in a-manner similar to that illustrated in Figures 2 and 3, so that they hang freely. They may form part of the boiler surfaces or provide a heat exchanger for any other purpose. In any event, a suitable coolant is circulated through the serpentine coils or tubes.

Inasmuch as the serpentine coils consist substantially entirely of elongated vertical members which are merely joined at their upper and lower ends by U-shaped bends, verylittle of the surface of these coils is not vertical. Asa consequence, the 'fiy-ash accumulating on these non-vertical portions of the tubes covers but a very small part of the total area of the tubes, so that even though the agitation or shaking of the tubes employed to dislodge accumulated fiy-ash therefrom may not succeed in removing all of the accumulation from these curved surfaces the retention of the accumulation on these small surfaces does not seriously lower the cooling efliciency of the tubes,

. arranged to be bodily agitated-or Shaken to To enable bodily shaking or agitating the tubes to dislodge accumulated fly-ash therefrom, the

tubes'are connected by rods 43, welded between adjacent tubes; and the foremost tubes have rod extensions 44 projecting through the front wall of the combustion chamber. These projecting rod extensions are therefore accessible to be acted upon by any suitable vibrating mechanism as for instance a hammer structure 45 adapted to be periodically lifted by mechanism (not shown) to" swing down and strike the ends of the rod 162(- tensions 44.

As will be readily apparent, the serpentine coils or .tubes 39 collectively form a labyrinth of passages through which the combustion gases must flow to leave the combustion chamber and enter Most of the sticky fiy-ash is thus the gas pass.

intercepted and accumulated on these tubes.

the same time the combustion gases are cooled and the fly-ash which escapes contact with the tubes 39 is cooled to the point of being frozen so that it will not readily adhere to subsequently 46, upon being dislodged therefrom, is free to fall down into the first collecting hopper 2!. In every instance, the dislodged fiy-ash breaks off in chunks or pieces of sufficient size and weight to fall. w thstandin he os ibl upward can rent of combustion gases.

s m n r of u portin t ser en ine oils u es not o low m to b haken or i t d ut lso s t e ad ed advanta e of iail t i r m l and repl cement th eo As shown in F u e le c e rent ne coil has e d conne ted to fe d n and receiving headrs F audit ocated abo e the to o the serpentine coi in ositio s si re ched u on ifti t e o wall '1 Lifti g the o wall so exp s a i he e enti e il Henc by er y utt n h e ds f a se cte Seren ine coil f itsheeders. this c l may be lifted ro i s s pp ting tu es 4.2 wi hout anywise disturbing the adjacent coils, and of course by the same token and with equal facility a new coil can be dropped into place and its ends welded to the headers.

The heat exchangers i7, [8,. l9 and 21! are all substantially of the same construction as that described, that is, they all consist of serpentine coils or tubes draped over supporting tubes and SP.- lodge accumulated fly-ash therefrom. The fly.- ash, scdislodged from these heat exchangers, falls into the hoppers 22, and 23. The specific use to which the heat exchangers l1, l8, l9 and 20 are put is a matter of choice but the first two H and "3) may be the convection part and the last two (l9 and 2B) the economizer part of the boiler.

The manner of agitating. or shaking the serpentine coils of the heat exchangers 46 differs slightly from that previously described. As best illustrated in Figure 2 this agitation is effected by transverse bars 4! extending into the gas pass and hooked onto the lower bends of the tubes as at 48. Preferably the bottom loops of alter.- nate tubes are'at a lower elevation than those of the intervening tubes and the agitating bars 47 are hooked only onto these lowermost bends.

Thus, upon reciprocation of the bars 47 in any suitable manner as by an eccentric 49, the tubes may be agitated to the point of collision with each other, thereby assuring the dislodge 1Z9 is of the same type a's'that hereinbefore described, that is, parallel horizontal main sup.- porting tubes 50 connected at their ends to headers 5| have a series of zigzag tubes 52 resting thereon and the serpentine coils are draped over these zigzag coils.

From the foregoing description taken in connection with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention affords a substantial improvement in the art of recovering valuable chemical constituents of waste liquors; and that it provides a substantial improvement in furnaces gen erally, and especially those adapted for such recovery processes.

What I claim as my invention is:

l. A combined waste heat boiler and chemical recovery unit comprising: means defining an upright combustion chamber having a ceiling; means for introducin chemical containing c0mbu'stibles into the combustion chamber to be burned therein and to have the chemical to be recovered accumulate upon the floor of the combustion chamber; means defining a discharge opening at the bottom of the combustion chamber from which the accumulated chemical may be discharged as a liquid; a plurality of substan- 7 tially horizontal boiler fluid containing tubes providing supporting members near the ceiling of the combustion chamber; a group of side-byside serpentine coils hanging from said support ing members with their legs vertical and 'substantially uniformly distributed across the horizontal area of the combustion chamber to provide-a maze of vertical cooling surfaces in the upper portion of the combustion chamber; headers at the top of the combustion chamber to which the ends of each serpentine coils are'connected and whereby boiler fluid may be circu l'ated through the serpentine coils; means-defining a gas pass leading from the upper portion of the combustion chamber, the entry to said gas pass being above the bottom of said group of serpentine coils so that the combustion gases leaving the combustion chamber must flow between said coils to reach the gas pass whereby chemical-containing fly ash entrained in said combustion gases impinges the coils m accumulate thereon; and means for vibrating said coils to dislodge accumulated fly ash from the coils in pieces of sufficient size and weight to drop to the bottom of the combustion chamber for reprocessing.

2. The structure set forth in claim 1 further characterized by the fact that the gas pass has a vertical'component alongside the combustion chamber and connected thereto at the top so that combustion gases entering the gas pass from the combustion chamber flow downwardly in said component of the gas pass; and further by the provision of'a collecting hopper at the bottom of the vertical component of the gas pass; and the l provision of a. group of hanging vibratable serpentine coils in the upper portion of the said vertical component of the gas pass as Well as in the upper portion of the combustion chamber.

3. In an apparatus of the character described: means defining an upright combustion chamber; means defining a'gas pass leading from the upper portion of the combustion chamber and through which combustion gases leave the com bustion chamber; a group of serpentine coils, each containing boiler fluid and having parallel legs alternately connectedat their opposite ends; a'plurality of boiler fluid containing tubes disposed substantially horizontally in the top of the combustion chamber; said serpentine coils being draped over the tubes to hang loosely therefrom with their legs vertical and substantially uniformly distributed across the entire ceiling of the combustion chamber and with the bottom of the coils extending a substantial distance below the entry to the gas pass so that the combustion gases leaving the combustion chamber must flow between the coils to reach the gas pass and whereby fly ash entrained in the gases impinges the coils to accumulate thereon; and means for vibrating said coils to dislodge accumulated fly ash from the coils in pieces of sufficient size and weight to drop to the bottom of the combustion chamber.

4. In a boiler having a combustion chamber, an intercepting unit adapted to intercept fly ash and the like entrained in the combustion gases leaving the combustion chamber, comprising a plurality of substantially horizontal boiler fluid containing tubes; inlet and outlet headers containing boiler fluid; a group of serpentine coils each connecting said headers and containing boiler fluid and each having parallel legs alternately connected at their .opposite ends, said serpentine coils being loosely hung from the substantially horizontal tubes to be supported thereby in a manner permitting vibration of the coils and bodily lifting of any coil ofi its supporting tubes without disturbing adjacent coils upon disconnection of said coil from the headers; and means for vibrating the dependent legs of the coils to dislodge accumulated fly ash therefrom.

DAVID DALIN.

REFERENCES CITED The following references are of record in the file of this patent:

TENTS 

1. A COMBINED WASTE HEAT BOILER AND CHEMICAL RECOVERY UNIT COMPRISING: MEANS DEFINING AN UPRIGHT COMBUSTION CHAMBER HAVING A CEILING; MEANS FOR INTRODUCING CHEMICAL CONTAINING COMBUSTIBLES INTO THE COMBUSTION CHAMBER TO BE BURNED THEREIN AND TO HAVE THE CHEMICAL TO BE RECOVERED ACCUMULATE UPON THE FLOOR OF THE COMBUSTION CHAMBER; MEANS DEFINING A DISCHARGE OPENING AT THE BOTTOM OF THE COMBUSTION CHAMBER FROM WHICH THE ACCUMULATED CHEMICAL MAY BE DISCHARGED AS A LIQUID; A PLURALITY OF SUBSTANTIALLY HORIZONTAL BOILER FLUID CONTAINING TUBES PROVIDING SUPPORTING MEMBERS NEAR THE CEILING OF THE COMBUSTION CHAMBER; A GROUP OF SIDE-BYSIDE SERPENTINE COILS HANGING FROM SAID SUPPORTING MEMBERS WITH THEIR LEGS VERTICAL AND SUBSTANTIALLY UNIFORMLY DISTRIBUTED ACROSS THE HORIZONTAL AREA OF THE COMBUSTION CHAMBER TO PROVIDE A MAZE OF VERTICAL COOLING SURFACES IN THE UPPER PORTION OF THE COMBUSTION CHAMBER; HEADERS AT THE TOP OF THE COMBUSTION CHAMBER TO WHICH THE ENDS OF EACH SERPENTINE COILS ARE CONNECTED AND WHEREBY BOILER FLUID MAY BE CIRCULATED THROUGH THE SERPENTINE COILS; MEANS DEFINING A GAS PASS LEADING FROM THE UPPER PORTION OF THE COMBUSTION CHAMBER, THE ENTRY TO SAID GAS PASS BEING ABOVE THE BOTTOM OF SAID GROUP OF SERPENTINE COILS SO THAT THE COMBUSTION GASES LEAVING THE COMBUSTION CHAMBER MUST FLOW BETWEEN SAID COILS TO REACH THE GAS PASS WHEREBY CHEMICAL-CONTAINING FLY ASH ENTRAINED IN SAID COMBUSTION GASES IMPINGES THE COILS TO ACCUMULATE THEREON; AND MEANS FOR VIBRATING SAID COILS OF DISLODGE ACCUMULATED FLY ASH FROM THE COILS IN PIECES OF SUFFICIENT SIZE AND WEIGHT TO DROP TO THE BOTTOM OF THE COMBUSTION CHAMBER FOR REPROCESSING. 